Getting Enough Vitamin D before and during Pregnancy

Women should ensure that they have a satisfactory level of vitamin D both before and during pregnancy. Pregnant adult women and nursing mothers need 600 IU of vitamin D every day, and teen mothers need 800 IU daily.

During pregnancy, a woman is eating for two. The growing fetus gets its nutrition entirely from the mother. If she doesn’t have what it needs, she can’t give it to the fetus. The fetal needs occur when the key structures of the fetus are being formed. Extreme deficiencies of important nutrients can cause deformities in the fetus; for example, folate deficiency causes neural tube defects.

How vitamin D influences a baby’s development

Scientists have long known that vitamin D’s greatest impact is on bone health. Keeping bones strong and healthy is especially important as infants and young children grow, but the foundation is established in the womb.

A problem with calcium, bones, or vitamin D in a baby's development doesn’t occur until months after birth (and often into the second year). After birth, the baby becomes dependent on calcitriol to absorb calcium from the intestines, and if that baby is vitamin D-deficient, not enough calcium gets into the skeleton and the soft bones of rickets can develop.

Getting enough vitamin D during pregnancy ensures that the baby is born with a good 25-hydroxyvitamin D level and is, therefore, well prepared to absorb needed calcium from breast milk or baby formula.

Preparing for a pregnancy with vitamin D

Certain groups of women are at higher risk of having low levels of vitamin D:

Women with darker skin

Women who live in northern regions during the winter

Women who cover their skin for religious or cultural purposes

Even before a woman becomes pregnant, she must have a satisfactory level of vitamin D for a number of reasons:

In experimental animals, the onset of the reproductive cycle is delayed in females who are deficient in vitamin D because calcium metabolism is upset when vitamin D isn’t present. This is why fertility is lower when vitamin D is deficient.

Starting with healthy levels of vitamin D ensures that the fetus gets enough from the mother. Blood levels of 25-hydroxyvitamin D in the fetus are 75 to 100 percent of the mother’s value because that form of vitamin D passes readily across the placenta.

The following adverse health outcomes for the baby have been linked to severely low levels of vitamin D in the mother:

Low birth weight

Low blood calcium in the days after birth (but not at birth)

Poor growth after birth

Bone fragility developing after birth (but not at birth)

Increased incidence of immune diseases like type 1 diabetes later in childhood

These adverse effects are probably due in part to the mother’s health before and during pregnancy: If her vitamin D intake is poor, her overall nutrition and socioeconomic status are likely not good, and she’s less likely to have access to prenatal care. If the mother has severe vitamin D deficiency with osteomalacia and inflamed or weakened muscles (myopathy), then those weak muscles mean she will have trouble with labor and delivery.

The conditions that caused the mother to have low vitamin D status before and during pregnancy are likely to continue after the baby is born, such that the child shares low vitamin D status and is at higher risk for developing medical conditions that might be caused by low vitamin D.

Getting enough vitamin D for two during pregnancy

If a woman has enough vitamin D before pregnancy and she gets pregnant, she needs to continue to take sufficient vitamin D for her needs and those of the fetus. However, in some groups, like African Americans, 70 percent of women who are pregnant have low serum vitamin D levels.

Women who fail to get enough vitamin D during their pregnancy may develop complications. Some studies show that there are associations between serum vitamin D levels and diseases of pregnancy like preeclampsia (high blood pressure and protein in the urine) and gestational diabetes (diabetes that begins during the stresses of pregnancy).

Women with 25-hydroxyvitamin D less than 15 ng/ml (37.5 nmol/L) have Caesarean sections four times as often as women with a higher level. It just isn’t clear if low vitamin D levels are the cause or general markers of poor health.

If you’re pregnant, you can get your vitamin D from a combination of sun and supplements. Avoid fish with mercury, but enjoy other foods that contain some vitamin D like milk or fortified breakfast cereal.

Exposure to low levels of vitamin D in the womb may predispose the fetus to develop certain conditions later in childhood, such as lower bone mass/density, type 1 diabetes, and other autoimmune conditions. It’s clearly important for a pregnant woman to maintain 25-hydroxyvitamin D levels over 20 ng/ml (50 nmol/L) so the baby is born with a similar level.